Millions of people could lose power across North and SC.
The Miami-based center says the center of the eye moved ashore with top sustained winds of 90 miles per hour (150 kph), making Florence a Category 1 hurricane in terms of wind intensity.
Its storm surge and the prospect of 1 to 3 1/2 feet of rain were considered a bigger threat than its winds, which dropped off from an alarming 140 miles per hour - Category 4 - earlier in the week.
"Some of the rainfall totals we're getting are already adding up to about 14 inches", NHC Director Ken Graham said shortly after 11 a.m. ET.
And as the storm pushes inland, it could dump 6-10 inches as far inland as Charlotte and Raleigh in North Carolina as well as in Roanoke, Virginia, he said.
The National Hurricane Center said Florence will eventually make a right hook to the northeast over the southern Appalachians, moving into the mid-Atlantic states and New England as a tropical depression by the middle of next week.
The U.S. military says a massive relief effort is ready to sweep into affected areas to deliver food and water, conduct search and rescue missions, as well as provide medical care and restore power. Hurricane Florence hit Wilmington as a category 1 storm causing widespread damage and flooding along the Carolina coastline.
The bulk of the three media briefings held by police chief Dan House surrounded how they were still anticipating the serious and catastrophic storm surge as well as hurricane force winds.
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In a hurricane, as Live Science has reported, the most significant threat is flooding, not the high winds.
WTOP's Steve Dresner, who is in Morehead City, North Carolina, described the scene just after 10 p.m. Thursday: "I'm looking out a fourth floor balcony back to the center of Morehead City, and the lights are out".
Municipal power agencies are reporting few outages, except New Bern, which had 17,820 customers without power, according to ElectriCities, the organization that supports the local power agencies.
Winds and rain were arriving later in SC, and a few people were still walking on the sand at Myrtle Beach while North Carolina was getting pounded.
More than 12,000 were in shelters in North Carolina. "Trees are blowing down in the wind".
Florence is expected to produce heavy and excessive rainfall into coastal North Carolina, with the possibility of it stretching into the far northeastern portion of SC, the NHC said.
The downtown area of the city of 30,000 people was underwater and around 150 people were waiting to be rescued, city authorities said on Twitter.
More than 3,000 inmates at North Carolina prisons and juvenile detention centers were moved out of the storm's path.
In Hampton Roads, a tropical storm warning is in effect from Poquoson to the Virginia-North Carolina border, including the lower James and York rivers.